Photo-degradation of dexamethasone phosphate using UV/Iodide process: Kinetics, intermediates, and transformation pathways

Abstract This study aims to develop a UV/Iodide process, as a novel procedure of Advanced Reduction Processes (ARPs), and utilized it for photo-degradation, detoxification and mineralization of dexamethasone phosphate (DexP) in aqueous Solution. UV irradiation utilization leads to DexP photo-degradation of 27%, 49% and 60% after the photo-degradation within 2.5, 7.5 and 15 min reaction time, respectively. Also, with UV/Iodide process photo-degradation of DexP increased to 42, 71, and 82% in 2.5, 7.5 and 15 min reaction time, respectively. Therefore, the 2:0.9 molar ratio was chosen as the optimal and practical DexP / Iodide molar ratio to operate the main UV/Iodide processes. Since the concentration of DexP increased from 10 to 75 mg L−1, the kobs and robs values of the process, respectively alter from 0.1987 to 0.0486 min−1 and from 1.987 to 5.94 mg L−1 min−1. Also, kobs and robs values were decreasing in 100 mg L−1 to 0.0323 min−1 and 3.23 mg L−1 min−1, respectively. Also, changes in the DexP concentration from 10 to 100 mg L−1, EEo increases from 1.45 to 8.95 (kinetic model) and 0.71–1.18 to 2.02–4.13 (figure of merit model) kW h m−3. The UV/Iodide effluent was sampled at the photoreaction times of 5 to 15 min and analyzed by LC-MS, to find the intermediates and possible pathways of DexP photo-degradation in the UV/Iodide process. Information from LC-MS indicated in first step DexP converts to compounds with a breaking ring through the attack of the reducer agents and, then, it degrades into linear compounds. Then, these breaking ring compounds are converted into simpler compounds such as acetic acid and formaldehyde. Ultimately, the linear intermediate are mineralized into CO2, and H2O. UV/Iodide process decreases the COD and TOC level about 70% and 74% within the photoreaction time 40 min, respectively.